Optical measurement systems are used for e.g. analysing properties or material contents of a target. Such optical measurement systems typically measure absorbance, reflection or emission of a target. The measurement systems usually have filters in order to facilitate the measurements with specified radiation wavelengths. Such filters can be controllable Fabry-Perot interferometers, for example.
It is often necessary to provide measurements of a target with two or more wavelengths. When such measurements are made successively the measurement tends to take a long time. Document FI119830B1 discloses a system for optical measurement where radiation of several wavelengths is measured simultaneously. This system requires a radiation detector which has detector elements with different spectral sensitivities. Document GB2445956A discloses another measurement system where several wavelengths can be measured simultaneously. Radiation sources of different wavelengths are modulated, and the detected radiation is demodulated in order to separate the signals that correspond to the different wavelengths.
It is often also necessary to measure a large number of samples, especially in the field of pharmaceutical testing. This is usually done by providing the measurements for one sample at a time, and changing the sample under measurement by moving a sample tray. This way, however, providing the measurements for a large number of samples takes a long time. It is possible to use an image detector and measure several samples simultaneously. However, such image detectors which qualify for accurate optical measurements are expensive. Especially, suitable low-cost image detectors for measuring radiation of long wavelengths such as NIR need to be measured.